Chlorine dioxide has been extensively investigated for many years and has found wide use both as a disinfectant and as a chemical oxidizer. It can be applied in a broad range of water treatment applications for each purpose.
One process for producing chlorine dioxide has been by the reaction of a chlorate salt with an acid, e.g., the reaction of sodium chlorate with sulfuric and hydrochloric acids. In this regard there has also been investigated the production of chloric acid from chlorate salts. The chloric acid could then be utilized in various generating systems which produce chlorine dioxide product. These generating systems are well known and are generally well developed commercially, such as for the pulp bleaching industry.
One method for producing chloric acid and subsequently reducing it to produce chlorine dioxide has been disclosed in U.S. Pat. No. 3,810,969. In this patent it is taught that initially chloric acid can be produced by contacting a metal chlorate with an ion exchange resin and thereafter the resulting chloric acid reduced with a conventional reducing agent in a strong mineral acid medium.
More recently, catalytic processes have been investigated for generating chlorine dioxide. Such systems have been researched in regard to employing feedstocks that are aqueous solutions of chlorate salts. Included in these various investigations has been the utilization of an electrochemical cell having active cathodes bearing special electrocatalytic coatings. In U.S. Pat. No. 4,426,263 it has been taught to combine a chlorate compound feedstock with an aqueous strong acid feedstock and to electrolyze the combined material in an electrochemical cell. The cell contains electrocatalytic cathodes that can have a coating of mixed metal oxides. By this process chlorine dioxide is directly prepared from the chlorate salt.
Because of its wide commercial acceptance, it would still be desirable to produce chlorine dioxide efficiently and economically without either deleterious by-products or by-products that are difficult to utilize or dispose of. It also would be highly desirable to provide such a system that could efficiently generate chlorine dioxide while offering economy of recycle to maximize chlorate utilization.